LOCALIZATION STUDIES OF IGFBP-2 AND IGFBP-5 IN THE ANTERIOR COMPARTMENT OF THE EYE

Purpose. Insulin-like growth factor binding proteins (IGFBPs) may modu late insulin-like growth factor-I (IGF-I) action and are important reg ulating factors in the IGF system. Our aim was to determine the presen ce of IGFBP-2 and -5 in the anterior compartment of the eye and to com pare the histological sites of these IGFBP proteins with the respectiv e IGFBP mRNAs. Methods. To investigate this, immunohistochemistry was used to detect the presence of IGFBP-2 and -5 proteins, and in situ hy bridization was used to determine the presence of IGFBP-2 and -5 mRNAs . The studies were performed in normal adult male Sprague-Dawley rats. Immunohistochemistry was performed by the immunoperoxidase method wit h polyclonal antibovine-IGFBP-2 and antihuman-IGFBP-5 antibodies, In s itu hybridization was performed using S-35-radiolabelled riboprobes. R esults. IGFBP-2 mRNA and protein were demonstrated in the outer non-pi gmented ciliary epithelium, the corneal germinal epithelium and the co rneal endothelium. IGFBP-2 mRNA was detected in these same histologica l layers of the ciliary processes and the cornea. IGFBP-5 mRNA localiz ed to the stroma and also to the inner pigmented ciliary epithelium an d IGFBP-5 protein was demonstrated in the adjacent outer nonpigmented ciliary epithelium. IGFBP-5 mRNA and protein were not demonstrated in the cornea. IGFBPs-2 and -5 were not demonstrated by immunohistochemis try in other structures of the eye. Conclusion. We have shown co-local ization of IGFBP-2 mRNA and protein and adjacent cellular localization of IGFBP-5 mRNA and proteins in the anterior compartment of the eye. The presence of IGFBP-2 and -5 in the outer ciliary epithelium suggest s secretion into the aqueous humour, where they may enhance trapping o f IGF-I which may be important for lens and corneal cell survival, Our studies outlining the site of locally synthesized IGFBPs suggests spe cific roles in regulation of IGFs and highlights the potential importa nce of the IGF system in the eye.